Semiconductor module

ABSTRACT

A semiconductor module according to embodiments includes a first external terminal, a second external terminal, a first semiconductor switch which is electrically connected between the first external terminal and the second external terminal and includes a first gate electrode, a second semiconductor switch which is electrically connected in parallel with the first semiconductor switch, between the first external terminal and the second external terminal, and includes a second gate electrode, a first fuse electrically connected between the first external terminal and the first semiconductor switch, and a second fuse electrically connected between the second external terminal and the first semiconductor switch.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-173119, filed on Sep. 14, 2018, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor module.

BACKGROUND

A power module includes a plurality of semiconductor switching elementsmounted on a substrate, for example.

In a power module including a plurality of semiconductor switchingelements, in a case where one semiconductor switching element isshort-circuited and fails during operation, power control with a powermodule cannot be continued. Further, at a spot where a short-circuitfailure is caused, a large quantity of heat is generated due toconcentration of currents or occurrence of a persistent arc. For thosereasons, a serious secondary disaster such as a fire may possibly beinvited.

In order to prevent occurrence of a serious secondary disaster, a powerapparatus such as an inverter circuit including a power module isprovided with an overcurrent protection function in some cases. With anovercurrent protection function, when an abnormal current caused due toa short-circuit failure is detected, an operation of a power apparatusis stopped after a previously-set time period. By stopping an operationof a power apparatus, it is possible to reduce a risk of a secondarydisaster. However, after an operation of a power apparatus is stopped,it becomes necessary to replace a power module and restart a powerapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an equivalent circuit of a semiconductor moduleaccording to a first embodiment;

FIG. 2 is a schematic top view of the semiconductor module according tothe first embodiment;

FIG. 3 is a schematic sectional view of the semiconductor moduleaccording to the first embodiment;

FIGS. 4A, 4B, and 4C are schematic views of a fuse according to thefirst embodiment;

FIG. 5 is a schematic view of the fuse according to the firstembodiment;

FIG. 6 is an explanatory view for a function and an effect of thesemiconductor module according to the first embodiment;

FIG. 7 is a diagram of an equivalent circuit of a test circuit in anexample of experiment in the first embodiment;

FIGS. 8A, 8B, 8C, and 8D are views showing results of a test in theexample of experiment in the first embodiment;

FIG. 9 is a diagram of an equivalent circuit of a semiconductor moduleaccording to a second embodiment;

FIG. 10 is a schematic top view of the semiconductor module according tothe second embodiment;

FIG. 11 is a diagram of an equivalent circuit of a test circuit in afirst example of experiment in the second embodiment;

FIG. 12 is a view showing results of measurement in the first example ofexperiment in the second embodiment;

FIG. 13 is a diagram of an equivalent circuit of a test circuit in asecond example of experiment in the second embodiment;

FIG. 14 is a view showing results of measurement in the second exampleof experiment in the second embodiment;

FIG. 15 is a diagram of an equivalent circuit of the semiconductormodule according to a modification of the second embodiment;

FIG. 16 is a diagram of an equivalent circuit of a test circuit in anexample of experiment in the modification of the second embodiment;

FIG. 17 is a view showing results of measurement in the example ofexperiment in the modification of the second embodiment;

FIG. 18 is a diagram of an equivalent circuit of a semiconductor moduleaccording to a third embodiment; and

FIG. 19 is a schematic top view of the semiconductor module according tothe third embodiment.

DETAILED DESCRIPTION

A semiconductor module according to one aspect of the present disclosureincludes a first external terminal, a second external terminal, a firstsemiconductor switch which is electrically connected between the firstexternal terminal and the second external terminal and includes a firstgate electrode, a second semiconductor switch which is electricallyconnected in parallel with the first semiconductor switch between thefirst external terminal and the second external terminal, and includes asecond gate electrode, a first fuse electrically connected between thefirst external terminal and the first semiconductor switch, and a secondfuse electrically connected between the second external terminal and thefirst semiconductor switch.

In the present specification, components which are the same or aresimilar to each other are denoted by the same reference signs, andduplicated description will be omitted in some portions.

In the present specification, in order to indicate a positionalrelationship between components or the like, an upward direction and adownward direction in the drawing will be described as “upper” and“lower”, respectively, in some portions. In the present specification,concepts of “upper” and “lower” are not necessarily terms describing arelationship with a direction of gravity.

In the present specification, a “semiconductor module” means asemiconductor product in which a plurality of semiconductor elements aremounted in one package. A “semiconductor module” is a conceptual matterencompassing also an intelligent power module (IPM) in which a powersemiconductor element, a driver circuit, and a control circuit aremounted in one package, for example.

First Embodiment

A semiconductor module according to a first embodiment includes a firstexternal terminal, a second external terminal, a first semiconductorswitch which is electrically connected between the first externalterminal and the second external terminal and includes a first gateelectrode, a second semiconductor switch which is electrically connectedin parallel with the first semiconductor switch between the firstexternal terminal and the second external terminal, and includes asecond gate electrode, a first fuse electrically connected between thefirst external terminal and the first semiconductor switch, and a secondfuse electrically connected between the second external terminal and thefirst semiconductor switch.

FIG. 1 is a diagram of an equivalent circuit of the semiconductor moduleaccording to the first embodiment.

The semiconductor module according to the first embodiment is a powermodule 100 in which a plurality of power semiconductor elements aremounted in one package. The power module 100 is used for an inverterdesigned to control high power, or the like, for example. A ratedvoltage of the power module 100 is equal to or higher than 250 V andequal to or lower than 10 kV, for example.

In the power module 100, as shown in FIG. 1, a transistor T1 (firstsemiconductor switching element, i.e. a first semiconductor switch), atransistor T2 (second semiconductor switching element, i.e. a secondsemiconductor switch), a transistor T3 (third semiconductor switchingelement, i.e. a third semiconductor switch), and a transistor T4 (fourthsemiconductor switching element, i.e. a fourth semiconductor switch) areconnected in parallel between a negative-pole terminal N (first externalterminal) and a positive-pole terminal P (second external terminal).Each of the transistor T1, the transistor T2, the transistor T3, and thetransistor T4 is a metal oxide field effect transistor (MOSFET), forexample. A semiconductor switching element (semiconductor switch) may bean insulated gate bipolar transistor (IGBT) or a MOSFET.

The transistor T1 includes a source electrode S1, a drain electrode D1,and a gate electrode G1 (first gate electrode). The transistor T2includes a source electrode S2, a drain electrode D2, and a gateelectrode G2 (second gate electrode). The transistor T3 includes asource electrode S3, a drain electrode D3, and a gate electrode G3(third gate electrode). The transistor T4 includes a source electrodeS4, a drain electrode D4, and a gate electrode G4.

A fuse FU1 (first fuse) is electrically connected between thenegative-pole terminal N and the transistor T1. One end of the fuse FU1is electrically connected to the negative-pole terminal N, and the otherend is electrically connected to the source electrode S1 of thetransistor T1. A fuse FU2 (second fuse) is electrically connectedbetween the positive-pole terminal P and the transistor T1. One end ofthe fuse FU2 is electrically connected to the positive-pole terminal P,and the other end is electrically connected to the drain electrode D1 ofthe transistor T1.

A fuse FU3 (third fuse) is electrically connected between thenegative-pole terminal N and the transistor T2. One end of the fuse FU3is electrically connected to the negative-pole terminal N, and the otherend is electrically connected to the source electrode S2 of thetransistor T2. A fuse FU4 (fourth fuse) is electrically connectedbetween the positive-pole terminal P and the transistor T2. One end ofthe fuse FU4 is electrically connected to the positive-pole terminal P,and the other end is electrically connected to the drain electrode D2 ofthe transistor T2.

A fuse FU5 is electrically connected between the negative-pole terminalN and the transistor T3. One end of the fuse FU5 is electricallyconnected to the negative-pole terminal N, and the other end iselectrically connected to the source electrode S3 of the transistor T3.A fuse FU6 is electrically connected between the positive-pole terminalP and the transistor T3. One end of the fuse FU6 is electricallyconnected to the positive-pole terminal P, and the other end iselectrically connected to the drain electrode D3 of the transistor T3.

A fuse FU7 is electrically connected between the negative-pole terminalN and the transistor T4. One end of the fuse FU7 is electricallyconnected to the negative-pole terminal N, and the other end iselectrically connected to the source electrode S4 of the transistor T4.A fuse FU8 is electrically connected between the positive-pole terminalP and the transistor T4. One end of the fuse FU8 is electricallyconnected to the positive-pole terminal P, and the other end iselectrically connected to the drain electrode D4 of the transistor T4.

FIG. 2 is a schematic top view of the semiconductor module according tothe first embodiment. FIG. 3 is a schematic sectional view of thesemiconductor module according to the first embodiment. FIG. 3 shows asection taken along a line A-A′ in FIG. 2.

The power module 100 includes a resin case 10, a lid 12, a gate terminal20, a metal substrate 22, a resin insulating layer 24, a source wiringmetal layer 26, a drain wiring metal layer 28, gate wiring metal layers30 a to 30 d, drain connection metal layers 32 a to 32 d, sourceconnection metal layers 34 a to 34 d, a bonding wire 40, and a siliconegel 42 (sealing material).

FIG. 2 is a top view of the power module 100 in a state where the lid 12and the silicone gel 42 are removed.

The transistors T1 to T4 are vertical MOSFETs, for example. Thetransistors T1 to T4 are semiconductor chips using silicon carbide (SiC)or silicon (Si), for example.

In respective upper portions of the transistors T1 to T4, the sourceelectrodes S1 to S4 and the gate electrodes G1 to G4 are provided. Inrespective lower portions of the transistors T1 to T4, the drainelectrodes D1 to D4 are provided. For example, in the transistor T1, thesource electrode S1 and the gate electrode G1 are provided in an upperportion and the drain electrode D1 is provided in a lower portion.

The metal substrate 22 is copper, for example. When the power module 100is mounted in a power apparatus, a heat dissipation plate not shown inthe drawing is connected to a back surface of the metal substrate 22,for example.

The resin case 10 is provided around the metal substrate 22. The lid 12is provided on the resin case 10. Also, the inside of the power module100 is filled with the silicone gel 42 as a sealing material. The resincase 10, the metal substrate 22, the lid 12, and the silicone gel 42have functions of protecting or insulating components in the powermodule 100.

In an upper portion of the resin case 10, the negative-pole terminal N,the positive-pole terminal P, and the gate terminal 20 are provided. Anegative voltage, for example, is externally applied to thenegative-pole terminal N. A ground potential, for example, is applied tothe negative-pole terminal N. A positive voltage, for example, isexternally applied to the positive-pole terminal P.

The resin insulating layer 24 is provided on the metal substrate 22. Theresin insulating layer 24 has a function of insulating the metalsubstrate 22, the source wiring metal layer 26, the drain wiring metallayer 28, the gate wiring metal layers 30 a to 30 d, the drainconnection metal layers 32 a to 32 d, and the source connection metallayers 34 a to 34 d. A resin in the resin insulating layer 24 contains afiller which is formed of boron nitride, for example, and has highthermal conductivity.

The source wiring metal layer 26, the drain wiring metal layer 28, thegate wiring metal layers 30 a to 30 d, the drain connection metal layers32 a to 32 d, and the source connection metal layers 34 a to 34 d areprovided on the resin insulating layer 24. The source wiring metal layer26, the drain wiring metal layer 28, the gate wiring metal layers 30 ato 30 d, the drain connection metal layers 32 a to 32 d, and the sourceconnection metal layers 34 a to 34 d are provided in nearly the samesurface. The source wiring metal layer 26, the drain wiring metal layer28, the gate wiring metal layers 30 a to 30 d, the drain connectionmetal layers 32 a to 32 d, and the source connection metal layers 34 ato 34 d are copper, for example.

The source wiring metal layer 26, the drain wiring metal layer 28, thedrain connection metal layers 32 a to 32 d, and the source connectionmetal layers 34 a to 34 d have functions of electrically connecting thetransistors T1 to T4 to the negative-pole terminal N or thepositive-pole terminal P, for example. The gate wiring metal layers 30 ato 30 d have functions of connecting the transistors T1 to T4 to thegate terminal 20, for example.

The transistors T1 to T4 are provided on the drain connection metallayers 32 a to 32 d, respectively. The drain electrodes D1 to D4 of thetransistors T1 to T4 are connected to the drain connection metal layers32 a to 32 d using solder or Ag nanoparticles, for example.

The source electrodes S1 to S4 are connected to the source connectionmetal layers 34 a to 34 d using the bonding wire 40. The gate electrodesG1 to G4 are connected to the gate wiring metal layers 30 a to 30 dusing the bonding wire 40.

One ends of the fuses FU1, FU3, FU5, and FU7 are connected to the sourcewiring metal layer 26, and the other ends are connected to the sourceconnection metal layers 34 a to 34 d. One ends of the fuse FU2, FU4,FU6, and FU8 are connected to the drain connection metal layers 32 a to32 d, and the other ends are connected to the drain wiring metal layer28.

The source wiring metal layer 26 is connected to the negative-poleterminal N using the bonding wire 40. The drain wiring metal layer 28 isconnected to the positive-pole terminal P using the bonding wire 40.

The bonding wire 40 is a wire including aluminum or copper as a mainingredient, for example.

The transistors T1 to T4 and the fuses FU1 to FU8 are covered with thesilicone gel 42.

FIGS. 4A, 4B, and 4C are schematic views of the fuse according to thefirst embodiment. FIG. 4A is a top view, FIG. 4B is a sectional viewtaken along a line B-B′ in FIG. 4A, and FIG. 4C is a sectional viewtaken along a line C-C′ in FIG. 4A.

Each of the fuses FU1 to FU8 includes an insulating layer 80, a linearconductor 82, a first electrode pad 84, and a second electrode pad 86.The insulating layer 80 is one example of each of a first insulatinglayer and a second insulating layer. The linear conductor 82 is oneexample of each of a first linear conductor and a second linearconductor.

When a current having a predetermined value or larger flows in each ofthe fuses FU1 to FU8, the linear conductor 82 is cut because of Jouleheat, so that electrical continuity at opposite ends of each of thefuses FU1 to FU8 is interrupted.

The insulating layer 80 is formed of a material having an insulatingproperty. The insulating layer 80 functions as a supporting substratefor the linear conductor 82, the first electrode pad 84, and the secondelectrode pad 86.

The insulating layer 80 (first insulating layer) is glass or ceramic,for example. The insulating layer 80 is a resin such as an epoxy resin,a phenol resin, polyimide, or a fluorine-based resin, for example. Aresin mixed with an insulating filler particle or an insulating fibercan be used for the insulating layer 80. An insulating filler particleis silica, alumina, or aluminum nitride, for example. Also, aninsulating fiber is a glass fiber, for example.

A length L1 of the insulating layer 80 is equal to or larger than 1 mmand equal to or smaller than 20 mm, for example. A thickness t1 of theinsulating layer 80 is equal to or larger than 0.1 mm and equal to orsmaller than 1 mm, for example.

The linear conductor 82 is provided on the insulating layer 80. Thereare provided a plurality of linear conductors 82, for example. Thelinear conductors 82 are parallel with each other. FIG. 4A shows a casewhere five linear conductors 82 are provided, as an example. The numberof the linear conductors 82 is not limited to five, and there may beprovided a single linear conductor. Also, two, three, four, or six ormore linear conductors may be provided.

The linear conductor 82 is formed of a material having conductivity. Thelinear conductor 82 is a metal, for example. The linear conductor 82 isa metal containing one of copper, copper alloy, aluminum, aluminumalloy, tin, zinc, bismuth, and nickel, as a main ingredient. The linearconductor 82 can be configured as a stacked structure including twokinds of metals, for example.

A length L2 of the linear conductor 82 is equal to or larger than 0.25mm and equal to or smaller than 10 mm, for example. A thickness t2 ofthe linear conductor 82 is equal to or larger than 0.1 μm and equal toor smaller than 2 μm, for example.

A width w of the linear conductor 82 is equal to or larger than 10 μmand equal to or smaller than 1000 μm, for example. A space s between thelinear conductors 82 is equal to or larger than 10 μm and equal to orsmaller than 1000 μm, for example.

The first electrode pad 84 is provided at one end of the linearconductor 82, and the second electrode pad 86 is provided at the otherend of the linear conductor 82. The first electrode pad 84 and thesecond electrode pad 86 are provided in such a manner that the linearconductor 82 is interposed. The first electrode pad 84 and the secondelectrode pad 86 are connected to the linear conductor 82. The firstelectrode pad 84 and the second electrode pad 86 have functions ofapplying a voltage across one end and the other end of the linearconductor 82.

The first electrode pad 84 and the second electrode pad 86 are formed ofthe same material as the linear conductor 82, for example.

A protective insulating film not shown in the drawing can be provided onthe linear conductor 82. The protective insulating film is siliconoxide, silicon nitride, silicon oxynitride, or polyimide, for example.

The fuses FU1 to FU8 can be manufactured using a semiconductormanufacturing process, for example. A glass substrate, one example ofthe insulating layer 80, is prepared, for example. Then, a metal film isformed on the glass substrate by a sputtering process. The metal film ispatterned using a lithography process or a reactive ion etching process,so that a plurality of linear conductors 82, the first electrode pad 84,and the second electrode pad 86 are formed.

FIG. 5 is a schematic view of the fuse according to the firstembodiment. FIG. 5 shows a state in which the fuse FU1 is mounted in thepower module 100. The first electrode pad 84 of the fuse FU1 isconnected to the source wiring metal layer 26 via a first adhesion layer88 a. The second electrode pad 86 of the fuse FU1 is connected to thesource connection metal layer 34 a via a second adhesion layer 88 b. Thefirst adhesion layer 88 a and the second adhesion layer 88 b are solderor Ag nanoparticles, for example.

Below, a function and an effect of the power module 100 according to thefirst embodiment will be described.

In a power module including a plurality of semiconductor switchingelements (semiconductor switches), in a case where one semiconductorswitching element (semiconductor switch) is short-circuited and failsduring operation, power control cannot be continued. Further, at a spotwhere a short-circuit failure is caused, a large quantity of heat isgenerated due to concentration of currents or occurrence of a persistentarc. For those reasons, a serious secondary disaster such as a fire maypossibly be invited.

In order to prevent occurrence of a serious secondary disaster, a powerapparatus such as an inverter circuit including a power module isprovided with an overcurrent protection function in some cases. With anovercurrent protection function, when an abnormal current caused due toa short-circuit failure is detected, an operation of a power apparatusis stopped after a previously-set time period. By stopping an operationof a power apparatus, it is possible to reduce a risk of a secondarydisaster. However, after an operation of a power apparatus is stopped,it becomes necessary to replace a power module and restart a powerapparatus.

FIG. 6 is an explanatory view for a function and an effect of thesemiconductor module according to the first embodiment.

In the power module 100 according to the first embodiment, thetransistor T1, for example, includes the fuse FU1 and FU2 in such amanner that the transistor T1 is interposed between the fuses. Considera case where the transistor T1 is short-circuited and fails duringoperation of the power apparatus including the power module 100. In thiscase, a large current flows across the positive-pole terminal P and thenegative-pole terminal N through the transistor T1 which isshort-circuited and fails.

In such a case, a large current flows also in the fuse FU1 and the fuseFU2, and the linear conductor 82 of each of the fuse FU1 and the fuseFU2 is cut because of generated Joule heat. As a result of cutting ofthe linear conductor 82 of each of the fuse FU1 and the fuse FU2, acurrent flow through the transistor T1 is interrupted.

A current flow through the transistor T1 is interrupted before anovercurrent protection function of the power apparatus is performed, forexample. An overcurrent protection function of the power apparatus isactivated after a previously-set time period, to stop an operation ofthe power apparatus. It is general that a previously-set time period isapproximately 10 μsec., for example.

The transistor T1 is separated from a circuit of the power module 100 bythe fuse FU1 and the fuse FU2. Thus, the power module 100 is allowed tooperate by the remaining transistors T2, T3, and T4. Accordingly, it ispossible to continue exercising power control with the power module 100.This makes it possible to continue operating the power apparatusincluding the power module 100. Therefore, reliability of the powerapparatus including the power module 100 is improved.

It is noted that in a case where the transistor T1 is short-circuitedand fails, the fuse FU1 and the fuse FU2 are blown out at the same time.If one of the fuses is not blown out, a current flow between the gateelectrode G1 and either the source electrode S1 or the drain electrodeD1 in the transistor T1 is left.

The gate electrode G1 is electrically connected to the gate electrodesG2 to G4 of the other transistors, a driver circuit outside the powermodule 100, and the like, for example. Accordingly, if a current flowbetween the gate electrode G1 and either the source electrode S1 or thedrain electrode D1 in the transistor T1 is left, it becomes difficult tocontinue exercising power control with the power module 100.

It is preferable that each of the fuses FU1 to FU8 included in the powermodule 100 has the following characteristics.

(First characteristic) To have a capability of accomplishinginterruption quickly in 10 μsec. or shorter. To interrupt a currentbefore an overcurrent protection function is activated, and make itpossible to continue operating the power apparatus including the powermodule 100.

(Second characteristic) To prevent occurrence of a persistent arc at atime of blowout. To prevent the power module 100 from being damaged dueto occurrence of a persistent arc.

(Third characteristic) To have a size equal to or smaller than a chipsize of a semiconductor switching element. To prevent a size of thepower module 100 from increasing due to mounting of a fuse.

(Fourth characteristic) To be blown out at the same time, in two fusesconnected in series. To interrupt a current flow toward a gateelectrode.

FIG. 7 is a diagram of an equivalent circuit of a test circuit in anexample of experiment in the first embodiment. The fuse FU1 and the fuseFU2 each having a configuration shown in FIGS. 4A to 4C were connectedin series, and a current load experiment in which a short circuit wassimulated by charge and discharge of a capacitor, was carried out.

In order to make a current flowing through each linear conductor when apower supply voltage is caused to vary between 1 and 3 kV, equal to 1 to80 A per linear conductor, the number of the linear conductors 82 wasset to one to ten, the thickness t2 of the linear conductor 82 was setto 0.35 μm, the width w of the linear conductor 82 was set to 3 to 850μm, and the space s between the linear conductors 82 was set to 3 to 140μm. The length L2 of the linear conductor 82 was caused to vary from 1mm to 2 mm, 3 mm, and 5 mm. The linear conductor 82 was configured as astacked structure including a titanium film and an aluminum film.

FIGS. 8A, 8B, 8C, and 8D are views showing results of a test in theexample of experiment in the first embodiment. FIG. 8A shows a casewhere L2 is equal to 1 mm, FIG. 8B shows a case where L2 is equal to 2mm, FIG. 8C shows a case where L2 is equal to 3 mm, and FIG. 8D shows acase where L2 is equal to 5 mm.

Shown are an applied voltage V01 applied to the fuse FU1 and the fuseFU2, a current (isolation current) per linear conductor 82, andoccurrence or non-occurrence of a persistent arc. An instance in which apersistent arc does not occur is indicated by a sign of a white circle,and an instance in which a persistent arc occurs is indicated by a signof a small cross. A hatched area is an area where a persistent arc doesnot occur at a time of blowout.

To set a current per linear conductor 82 to 40 A or smaller suppressesoccurrence of a persistent arc. Also, to increase the length L2 of thelinear conductor 82 results in an increase of the applied voltage V01 atwhich interruption can be accomplished without occurrence of apersistent arc. By setting the length L2 of the linear conductor 82 to 3mm or larger, it is possible to accomplish blowout at the appliedvoltage V01 of up to 3 kV.

It is noted that under each of the forgoing conditions, interruption canbe accomplished quickly in 10 μsec. or shorter. Also, under each of theforegoing conditions, the fuse FU1 and the fuse FU2 are cut at the sametime. Further, the length L2 of the linear conductor 82 is equal to orsmaller than 5 mm, so that a size equal to or smaller than a chips sizeof a semiconductor switching element is feasible.

The above-described example of experiment revealed that theabove-described (first characteristic), (second characteristic), (thirdcharacteristic), and (fourth characteristic) could be attained by thefuse according to the first embodiment.

It is preferable that the length L2 of the linear conductor 82 is equalto or larger than 1 mm and equal to or smaller than 10 mm, and it ismore preferable that the length L2 is equal to or larger than 3 mm andequal to or smaller than 5 mm. Within the above-described range,reduction of an applied voltage at which blowout can be accomplished canbe made smaller. Also, within the above-described range, a size of afuse can be further reduced.

It is preferable that the thickness t2 of the linear conductor 82 isequal to or larger than 0.1 μm and equal to or smaller than 2 μm, and itis more preferable that the thickness t2 is equal to or larger than 0.3μm and equal to or smaller than 1.0 μm. Within the above-describedrange, a larger current can be caused to flow during normal operation.Also, within the above-described range, reduction of an applied voltageat which blowout can be accomplished can be made smaller.

It is preferable that the width w of the linear conductor 82 is equal toor larger than 10 μm and equal to or smaller than 1000 μm, and it ismore preferable that the width w is equal to or larger than 20 μm andequal to or smaller than 200 μm. Within the above-described range, alarger current can be caused to flow during normal operation. Also,within the above-described range, reduction of an applied voltage atwhich blowout can be accomplished can be made smaller.

Also, it is preferable that each of the thickness t2 of the linearconductor 82 (first linear conductor) of the fuse FU1 and the thicknesst2 of the linear conductor 82 (second linear conductor) of the fuse FU2is equal to or larger than 0.1 μm and equal to or smaller than 1.3 μm,and that a difference between the thickness t2 of the linear conductor82 (first linear conductor) of the fuse FU1 and the thickness t2 of thelinear conductor 82 (second linear conductor) of the fuse FU2 is equalto or smaller than 0.3 μm. To set the thicknesses so as to fall withinthe above-described ranges makes it easy to blow out the fuse FU1 andthe fuse FU2 at the same time.

It is preferable that a rated current of the power module 100 is equalto or smaller than a value obtained by multiplication of the number ofthe linear conductors 82 by 40 A. To satisfy the above-describedcondition suppresses occurrence of a persistent arc at a time of blowingout a fuse.

It is preferable that a material forming the linear conductor 82 is ametal which is apt to be converted into a metal oxide by thermal energyproduced at a time of blowing out a fuse. By conversion into a metaloxide after blowout of a fuse, dielectric breakdown voltage is improved.From the foregoing viewpoint, it is preferable that a material formingthe linear conductor 82 includes aluminum.

As described above, with the semiconductor module according to the firstembodiment, it is possible to provide a semiconductor module which cancontinue operating even in a case where one semiconductor switchingelement is short-circuited and fails during operation. Accordingly, itis possible to continue operating the power apparatus including thesemiconductor module according to the first embodiment. Therefore,reliability of the power apparatus including the semiconductor moduleaccording to the first embodiment is improved.

Second Embodiment

A semiconductor module according to a second embodiment is differentfrom the semiconductor module according to the first embodiment in thatan overvoltage protection element electrically connected between eithera first external terminal or a second external terminal and a first gateelectrode is further included. Below, description of details which areto be duplication of the first embodiment will be partly omitted.

FIG. 9 is a diagram of an equivalent circuit of the semiconductor moduleaccording to the second embodiment.

The semiconductor module according to the second embodiment is a powermodule 200 in which a plurality of power semiconductor elements aremounted in one package.

In the power module 200, overvoltage protection elements 90 are providedbetween a negative-pole terminal N and a gate electrode G1, between thenegative-pole terminal N and a gate electrode G2, between thenegative-pole terminal N and a gate electrode G3, and between thenegative-pole terminal N and a gate electrode G4, respectively.

The overvoltage protection element 90 is an element in which acurrent-voltage characteristic is non-linear. The overvoltage protectionelement 90 is a two-terminal element in which resistance is reduced whenan applied voltage exceeds a predetermined threshold voltage. Theovervoltage protection element 90 has a function of causing a current toflow when an excessive voltage exceeding a predetermined thresholdvoltage is applied across two terminals. The overvoltage protectionelement 90 includes a first Zener diode Z1 and a second Zener diode Z2,for example.

The first Zener diode Z1 and the second Zener diode Z2 are connected inseries while being oriented reversely with respect to each other. Forexample, a cathode of the first Zener diode Z1 is connected to a cathodeof the second Zener diode Z2.

An anode of the first Zener diode Z1 is connected to the negative-poleterminal N. Also, an anode of the second Zener diode Z2 is connected toone of the gate electrode G1, the gate electrode G2, the gate electrodeG3, and the gate electrode G4.

FIG. 10 is a schematic top view of the semiconductor module according tothe second embodiment.

The power module 200 includes the negative-pole terminal N (firstexternal terminal), a positive-pole terminal P (second externalterminal), a transistor T1 (first semiconductor switching element, i.e.a first semiconductor switch), a transistor T2 (second semiconductorswitching element, i.e. a second semiconductor switch), a transistor T3(third semiconductor switching element, i.e. a third semiconductorswitch), a transistor T4 (fourth semiconductor switching element, i.e. afourth semiconductor switch), a fuse FU1 (first fuse), a fuse FU2(second fuse), a fuse FU3 (third fuse), a fuse FU4 (fourth fuse), a fuseFU5, a fuse FU6, a fuse FU7, a fuse FU8, and four pairs each includingthe first Zener diode Z1 and the second Zener diode Z2.

The power module 200 includes a resin case 10, a lid 12, a gate terminal20, a metal substrate 22, a resin insulating layer 24, a source wiringmetal layer 26, a drain wiring metal layer 28, gate wiring metal layers30 a to 30 d, drain connection metal layers 32 a to 32 d, sourceconnection metal layers 34 a to 34 d, diode connection metal layers 35 ato 35 d, a bonding wire 40, and a silicone gel 42 (sealing material).

FIG. 10 is atop view of the power module 200 in a state where the lid 12and the silicone gel 42 are removed.

The four pairs of the first Zener diodes Z1 and the second Zener diodesZ2 are provided on the diode connection metal layers 35 a to 35 d,respectively. The four pairs of the first Zener diodes Z1 and the secondZener diodes Z2 are connected to the diode connection metal layers 35 ato 35 d, respectively, using solder or Ag nanoparticles, for example.

Below, a function and an effect of the power module 200 according to thesecond embodiment will be described.

FIG. 11 is a diagram of an equivalent circuit of a test circuit in afirst example of experiment in the second embodiment. The fuse FU1 andthe fuse FU2 each having a configuration shown in FIGS. 4A to 4C wereconnected in series, and a current load experiment in which a shortcircuit was simulated by charge and discharge of a capacitor, wascarried out.

A voltage V02 of a wire between the fuse FU1 and the fuse FU2 wasmeasured. The voltage V02 of the wire between the fuse FU1 and the fuseFU2 represents a voltage of a gate electrode in a case where atransistor interposed between the fuse FU1 and the fuse FU2 isshort-circuited in an equivalent circuit of the power module 100 in FIG.1, in a simulated fashion.

FIG. 12 is a view showing results of measurement in the first example ofexperiment in the second embodiment. FIG. 12 shows variation with timeof the voltage V02.

In the circuit in FIG. 11, when a voltage is applied to the fuse FU1 andthe fuse FU2, the fuse FU1 and the fuse FU2 are blown out at the sametime. As shown in FIG. 12, the voltage V02 momentarily increases whenthe fuse FU1 and the fuse FU2 are blown out. In other words, a highvoltage is momentarily applied across the fuse FU1 and the fuse FU2. Itis considered that such application of high voltage is caused due to aninduced current generated by inductance of a circuit after the fuse FU1and the fuse FU2 are blown out.

Also in the equivalent circuit of the power module 100 in FIG. 1, a highvoltage may possibly be momentarily applied to a gate electrode in acase where a transistor interposed between the fuse FU1 and the fuse FU2is short-circuited. If a high voltage is momentarily applied to a gateelectrode, there is a fear of breakage of a circuit or an elementconnected to the gate electrode of the transistor. For example, a gatedriver circuit connected to the gate electrode, or a gate insulatingfilm in contact with a gate electrode of another transistor connected tothe gate electrode, may probably be broken.

FIG. 13 is a diagram of an equivalent circuit of a test circuit in asecond example of experiment in the second embodiment. In the circuitshown in FIG. 13, a wire which extends from between the fuse FU1 and thefuse FU2 and leads to a ground is provided in the circuit shown in FIG.11. Then, the wire is connected to the first Zener diode Z1 and thesecond Zener diode Z2 in series in such a manner that the diodes areoriented reversely with respect to each other. The circuit shown in FIG.13 is a result of simulating an equivalent circuit of the power module200 according to the second embodiment.

FIG. 14 is a view showing results of measurement in the second exampleof experiment in the second embodiment. FIG. 14 shows variation withtime of the voltage V02.

A momentary increase of the voltage V02 like that seen in the circuitshown in FIG. 11 in which the first Zener diode Z1 and the second Zenerdiode Z2 are not included is not observed. It is considered that acurrent flows to a ground by virtue of the first Zener diode Z1 and thesecond Zener diode Z2, so that an increase of a voltage is suppressed.

It is noted that each of the first Zener diode Z1 and the second Zenerdiode Z2 keeps having high resistance until an applied voltage reaches apredetermined threshold voltage, and thus, a level of a gate voltagebeing applied to a gate electrode of a transistor during normaloperation of the power module 200 is not affected.

With the power module 200 according to the second embodiment, in a casewhere a transistor is short-circuited, a circuit or an element connectedto a gate electrode of the short-circuited transistor is prevented frombeing broken. Hence, it is possible to continue operating the powerapparatus including the power module 200. Therefore, reliability of thepower apparatus including the power module 200 is further improved.

(Modification)

A semiconductor module according to a modification of the secondembodiment is different from that according to the second embodiment inthat a varistor is included in place of the first Zener diode Z1 and thesecond Zener diode Z2.

FIG. 15 is a diagram of an equivalent circuit of the semiconductormodule according to the modification of the second embodiment.

The semiconductor module according to the modification of the secondembodiment is a power module 201 in which a plurality of powersemiconductor elements are mounted in one package.

The power module 201 includes a varistor VA as the overvoltageprotection element 90. In the power module 201, the varistors VA areprovided as the overvoltage protection elements 90, between thenegative-pole terminal N and the gate electrode G1, between thenegative-pole terminal N and the gate electrode G2, between thenegative-pole terminal N and the gate electrode G3, and between thenegative-pole terminal N and the gate electrode G4, respectively.

FIG. 16 is a diagram of an equivalent circuit of a test circuit in anexample of experiment in the modification of the second embodiment. Thevaristor VA is connected to a wire which extends from between the fuseFU1 and the fuse FU2 and leads to a ground. The circuit in FIG. 16 is aresult of simulating an equivalent circuit of the power module 201according to the modification of the second embodiment.

FIG. 17 is a view showing results of measurement in an example ofexperiment in the modification of the second embodiment. FIG. 17 showsvariation with time of the voltage V02.

A momentary increase of the voltage V02 like that seen in the circuitshown in FIG. 11 in which the varistor VA is not included is notobserved. It is considered that a current flows to a ground by virtue ofthe varistor VA, so that an increase of a voltage is suppressed.

It is noted that the varistor VA keeps having high resistance until anapplied voltage reaches a predetermined threshold voltage, and thus, alevel of a gate voltage being applied to a gate electrode of atransistor during normal operation of the power module 201 is notaffected.

As described above, with the semiconductor modules according to thesecond embodiment and the modification, like the semiconductor moduleaccording to the first embodiment, it is possible to provide asemiconductor module which can continue operating even in a case whereone semiconductor switching element is short-circuited and fails duringoperation. Therefore, reliability of the power apparatus including thesemiconductor module according to the second embodiment is improved.Particularly, a circuit or an element connected to a gate electrode of ashort-circuited semiconductor switching element is prevented from beingbroken, so that reliability of the power apparatus including thesemiconductor module is further improved.

Third Embodiment

A semiconductor module according to a third embodiment is different fromthat of the first embodiment in that a third semiconductor switchingelement which is electrically connected in parallel with a firstsemiconductor switching element, between a first external terminal and asecond external terminal, and includes a third gate electrode is furtherincluded, a first fuse is electrically connected between the firstexternal terminal and the third semiconductor switching element, and asecond fuse is electrically connected between the second externalterminal and the third semiconductor switching element. Below,description of details which are to be duplication of the firstembodiment will be partly omitted.

FIG. 18 is a diagram of an equivalent circuit of the semiconductormodule according to the third embodiment.

The semiconductor module according to the third embodiment is a powermodule 300 in which a plurality of power semiconductor elements aremounted in one package. The power module 300 is used for an inverterdesigned to control high power, or the like, for example. A ratedvoltage of the power module 300 is equal to or higher than 250 V andequal to or lower than 10 kV, for example.

In the power module 300, as shown in FIG. 18, a transistor T1 (firstsemiconductor switching element, i.e. a first semiconductor switch), atransistor T2 (second semiconductor switching element, i.e. a secondsemiconductor switch), a transistor T3 (third semiconductor switchingelement, i.e. a third semiconductor switch), and a transistor T4 (fourthsemiconductor switching element, i.e. a fourth semiconductor switch) areconnected in parallel between a negative-pole terminal N (first externalterminal) and a positive-pole terminal P (second external terminal).Each of the transistor T1, the transistor T2, the transistor T3, and thetransistor T4 is a MOSFET, for example.

The transistor T1 includes a source electrode S1, a drain electrode D1,and a gate electrode G1 (first gate electrode). The transistor T2includes a source electrode S2, a drain electrode D2, and a gateelectrode G2 (second gate electrode). The transistor T3 includes asource electrode S3, a drain electrode D3, and a gate electrode G3(third gate electrode). The transistor T4 includes a source electrodeS4, a drain electrode D4, and a gate electrode G4.

A fuse FU1 (first fuse) is electrically connected between thenegative-pole terminal N and the transistor T1. The fuse FU1 (firstfuse) is electrically connected between the negative-pole terminal N andthe transistor T3. One end of the fuse FU1 is electrically connected tothe negative-pole terminal N, and the other end is electricallyconnected to the source electrode S1 of the transistor T1 and the sourceelectrode S3 of the transistor T3.

A fuse FU2 (second fuse) is electrically connected between thepositive-pole terminal P and the transistor T1. The fuse FU2 (secondfuse) is electrically connected between the positive-pole terminal P andthe transistor T3. One end of the fuse FU2 is electrically connected tothe positive-pole terminal P, and the other end is electricallyconnected to the drain electrode D1 of the transistor T1 and the drainelectrode D3 of the transistor T3.

The transistor T1 and the transistor T3 are connected in parallelbetween the fuse FU1 and the fuse FU2.

A fuse FU3 (third fuse) is electrically connected between thenegative-pole terminal N and the transistor T2. The fuse FU3 (thirdfuse) is electrically connected between the negative-pole terminal N andthe transistor T4. One end of the fuse FU3 is electrically connected tothe negative-pole terminal N, and the other end is electricallyconnected to the source electrode S2 of the transistor T2 and the sourceelectrode S4 of the transistor T4.

A fuse FU4 (fourth fuse) is electrically connected between thepositive-pole terminal P and the transistor T2. The fuse FU4 (fourthfuse) is electrically connected between the positive-pole terminal P andthe transistor T4. One end of the fuse FU4 is electrically connected tothe positive-pole terminal P, and the other end is electricallyconnected to the drain electrode D2 of the transistor T2 and the drainelectrode D4 of the transistor T4.

The transistor T2 and the transistor T4 are connected in parallelbetween the fuse FU3 and the fuse FU4.

FIG. 19 is a schematic top view of the semiconductor module according tothe third embodiment.

The power module 300 includes the negative-pole terminal N (firstexternal terminal), the positive-pole terminal P (second externalterminal), the transistor T1 (first semiconductor switching element,i.e. a first semiconductor switch), the transistor T2 (secondsemiconductor switching element, i.e. a second semiconductor switch),the transistor T3 (third semiconductor switching element, i.e. a thirdsemiconductor switch), the transistor T4 (fourth semiconductor switchingelement, i.e. a fourth semiconductor switch), the fuse FU1 (first fuse),the fuse FU2 (second fuse), the fuse FU3 (third fuse), and the fuse FU4(fourth fuse).

The power module 300 includes a resin case 10, a lid 12, a gate terminal20, a metal substrate 22, a resin insulating layer 24, a source wiringmetal layer 26, a drain wiring metal layer 28, gate wiring metal layers30 a to 30 d, drain connection metal layers 32 a and 32 b, sourceconnection metal layers 34 a and 34 b, a bonding wire 40, and a siliconegel 42 (sealing material).

The transistors T1 and T3 are provided on the drain connection metallayer 32 a in common. The transistors T2 and T4 are provided on thedrain connection metal layer 32 b in common.

The source electrodes S1 and S3 are connected to the source connectionmetal layer 34 a in common using the bonding wire 40. The sourceelectrodes S2 and S4 are connected to the source connection metal layer34 b in common using the bonding wire 40.

In the power module 300, the transistor T1 and the transistor T3 sharethe fuse FU1 and the fuse FU2. Then, the transistor T2 and thetransistor T4 share the fuse FU3 and the fuse FU4.

If the transistor T1 is short-circuited and fails, the fuse FU1 and thefuse FU2 are blown out. Also, if the transistor T3 is short-circuitedand fails, the fuse FU1 and the fuse FU2 are blown out.

If the transistor T2 is short-circuited and fails, the fuse FU3 and thefuse FU4 are blown out. Also, if the transistor T4 is short-circuitedand fails, the fuse FU3 and the fuse FU4 are blown out.

In the power module 300, two transistors share a fuse, so that thenumber of fuses in the power module 300 can be reduced. Accordingly,miniaturization of the power module 300 can be achieved.

As described above, with the semiconductor module according to the thirdembodiment, like the semiconductor module according to the firstembodiment, it is possible to provide a semiconductor module which cancontinue operating even in a case where one semiconductor switchingelement is short-circuited and fails during operation. Therefore,reliability of the power apparatus including the semiconductor moduleaccording to the third embodiment is improved. Further, by reduction ofthe number of fuses, miniaturization of a semiconductor module can beachieved.

Though the first to third embodiments have been described while taking acase in which four semiconductor switching elements are provided, as anexample, the number of semiconductor switching elements is not limitedto four as long as a plurality of semiconductor switching elements areprovided.

The first to third embodiments have been described while taking a casein which only a semiconductor switching element is included as asemiconductor element in a semiconductor module, as an example. However,the other semiconductor elements such as a diode, for example, may beincluded in a semiconductor module.

Though the first to third embodiments have been described while taking acase in which a semiconductor switching element is a MOSFET, as anexample, the other semiconductor switching elements such as an IGBT maybe applied as a semiconductor switching element.

Though the first to third embodiments have been described while taking asemiconductor module configured so as to include the resin case 10, asan example, a semiconductor module having a configuration in which asemiconductor switching element is formed by molding can be applied tothe present disclosure, for example.

Though the first to third embodiments have been described while taking acase in which the silicone gel 42 is used a sealing material, as anexample, the other resin materials such as an epoxy resin, for example,can be used in place of the silicone gel 42.

Though the second embodiment has been described while taking a case inwhich two Zener diodes are used as the overvoltage protection elements90, as an example, either one Zener diode or three or more Zener diodescan be used.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the semiconductor module describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the devices andmethods described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A semiconductor module comprising: a firstexternal terminal; a second external terminal; a first semiconductorswitch electrically connected between the first external terminal andthe second external terminal, the first semiconductor switch including afirst gate electrode; a second semiconductor switch electricallyconnected in parallel with the first semiconductor switch between thefirst external terminal and the second external terminal, the secondsemiconductor switch including a second gate electrode; a first fuseelectrically connected between the first external terminal and the firstsemiconductor switch; a second fuse electrically connected between thesecond external terminal and the first semiconductor switch; and anovervoltage protection element electrically connected between either thefirst external terminal or the second external terminal and the firstgate electrode, the overvoltage protection element including a varistor.2. The semiconductor module according to claim 1, wherein the first fuseincludes a first insulating layer and a plurality of first linearconductors on the first insulating layer, and the second fuse includes asecond insulating layer and a plurality of second linear conductors onthe second insulating layer.
 3. The semiconductor module according toclaim 2, wherein a length of each of the first linear conductors and thesecond linear conductors is equal to or larger than 1 mm and equal to orsmaller than 10 mm.
 4. The semiconductor module according to claim 2,wherein a thickness of each of the first linear conductors and thesecond linear conductors is equal to or larger than 0.1 μm and equal toor smaller than 1.3 μm, and a difference in the thickness between eachof the first linear conductors and each of the second linear conductorsis equal to or smaller than 0.3 μm.
 5. The semiconductor moduleaccording to claim 2, wherein each of the first linear conductors andthe second linear conductors includes aluminum.
 6. The semiconductormodule according to claim 1, further comprising: a third fuseelectrically connected between the first external terminal and thesecond semiconductor switch; and a fourth fuse electrically connectedbetween the second external terminal and the second semiconductorswitch.
 7. The semiconductor module according to claim 1 furthercomprising a third semiconductor switch electrically connected inparallel with the first semiconductor switch between the first externalterminal and the second external terminal, the third semiconductorswitch including a third gate electrode, wherein the first fuse iselectrically connected between the first external terminal and the thirdsemiconductor switch, and the second fuse is electrically connectedbetween the second external terminal and the third semiconductor switch.8. The semiconductor module according to claim 1 further comprising asealing material with which the first semiconductor switch, the secondsemiconductor switch, the first fuse, and the second fuse are covered.9. The semiconductor module according to claim 3, wherein a thickness ofeach of the first linear conductors and the second linear conductors isequal to or larger than 0.1 μm and equal to or smaller than 1.3 μm, anda difference in the thickness between each of the first linearconductors and each of the second linear conductors is equal to orsmaller than 0.3 μm.
 10. The semiconductor module according to claim 3,wherein each of the first linear conductors and the second linearconductors includes aluminum.
 11. The semiconductor module according toclaim 4, wherein each of the first linear conductors and the secondlinear conductors includes aluminum.